Anti-counterfeit techniques for preventing counterfeiting of articles require two features from the purposes thereof. The techniques firstly can easily perform authentication when consumers using an article verify whether the article is an authentic product from the perspective of security or the like of articles, and secondly can also perform more advanced authentication when it is necessary to distinguish an authentic article from sophisticated counterfeit products.
Presently, examples of anti-counterfeit techniques in widely use include watermark techniques, and holograms which allow users to determine authenticity with visual inspections. Although these techniques have an advantage in that they can be verified by visual inspections and thus can be easily authenticated, it is desirable to develop a new anti-counterfeit technique to meet demands for a more improved anti-counterfeit effect.
Thus, anti-counterfeit techniques of determining authenticity by making observation using a simple magnifying mechanism such as a loupe are gathering attention (Patent Literatures 1 to 3). In these techniques, since it is difficult to verify whether an anti-counterfeit technique is applied just at a glance, it is possible to obtain a higher anti-counterfeit effect as compared to anti-counterfeit techniques that can be verified with visual inspections. These techniques have another advantage in that they can be easily identified without requiring special devices and the like in determining authenticity.
As an anti-counterfeit technique that requires a magnifying mechanism when performing such authentication, a technique that uses microscopic particles called taggant particles (tracing additives) is proposed. In anti-counterfeit media using taggant particles, since the positions of taggant particles change among individual media, it is difficult to identify taggant particles themselves and duplicating is also difficult. Thus, the anti-counterfeit media have an excellent anti-counterfeit effect and individual medium can be identified.
Taggant particles having information that can be identified by magnifying and observing the same are known. Examples of such taggant particles include those having characters, symbols, emblems, and a special shape and those having special color information (Patent Literatures 4 and 5).
However, since taggant particles used conventionally are relatively easy to manufacture and high-resolution printing has become possible with progress of printing techniques, the risk of forgery is high when the formation positions of taggant particles are identified. Thus, it is requested to develop taggant particles having a higher anti-counterfeit effect.